1. Field of the Invention
This invention relates to angle transducers. In particular, it relates to an electro-optical means for measuring the rotational angle of one or more devices or to detect relative angular displacement between elements.
2. Description of the Prior Art
Transducers which function to convert amount and direction of rotational movement to electrical signals are particularly desirable for measurement and control. Various systems are known for detecting rotary movement and providing an electrical output proportional to the relative motion of two mechanical elements, such as shafts or the like. Prior art devices of the synchro type or of the type generating a series of pulses to be counted are known; however, these are bulky and relatively expensive.
Remote or optically-coupled rotational angle sensor systems presently available ordinarily employ space triangulation measurement techniques. These methods require simultaneous solutions to three-dimensional geometrical equations and involve use of extensive computer circuitry for obtaining the desired measurement. Rotational measurement in a single plane becomes a complex operation requiring much equipment when using this method. Angle measurement devices which are mechanically or electrically coupled to a rotating mechanism, such as used in servo loop follow-up or pick-off applications, are in frequent use.
The known types of angle rotation sensors can be replaced in many cases with an optically coupled measurement device described herein.
Previous techniques for sensing rotary angular position and for providing a reference input signal to system electronics, have required either direct electro-mechanical couplings to the rotary device or extensive computer mechanization for deriving position through optical triangulation methods. Optical measuring systems are available which utilize crossed linear polarizers for the purpose of detecting angle rotation. Various photoelectric, semiconductor or photosensitive elements are used for converting electromagnetic energy to a representative signal.
Typical prior art rotation detectors which employ crossed polarizers require careful matching of two or more sensors. In U.S. Pat. No. 3,474,255, a shaft mounted system employs two light polarizers angularly displaced by 90.degree. on one shaft. A third polarizer is mounted on another shaft. Light received by photocells from each of the displaced polarizers is converted to a current or voltage differential. The displacement or error signal is then used to drive a servo motor to keep the two shafts synchronized.
In U.S. Pat. No. 3,306,159, a polarizing sheet attached to a rotary member is illuminated by non-polarized light. A set of four orthogonally related polarizing filters have four associated photosensors. These sensors are connected in a bridge circuit which provides an output signal whose phase angle is representative of the rotation angle of the rotary member.
Angular measurement devices employing polarized radiation are also disclosed in U.S. Pat. Nos. 2,998,746 and 3,521,071.